430 FXUS63 KGLD 231127 AFDGLD Area Forecast Discussion National Weather Service Goodland KS 427 AM MST Sat Dec 23 2023 .SHORT TERM...(Today through Tuesday Morning) Issued at 330 AM MST Sat Dec 23 2023 Strong upper level low is developing and located over southern Arizona currently. Moisture is increasing in the upper levels currently as clouds streaming across western portions of the area. For today, continue to think that the majority of the day time hours will be dry, although some low chances at some showers and thunderstorms remains possible mainly south of Interstate 70 in western Kansas. Lightning and strong winds would be the primary hazards with the strongest updrafts. Wind gusts with any convection would be in the 45-55 mph range as fairly strong pressure falls around 5 mb looks to be present with this activity. Southerly winds will strengthen throughout the day gusting 30-40 mph by sunset. The main focus for this forecast package will be the snow and blowing snow potential that looks to begin overnight tonight. Overall expectations for timing remain on track as precipitation across east Colorado will start as rain briefly before quickly transitioning to all snow. Confidence is increasing in a convective snow band across NW portions of the area. Exact location of this band still remains in question but over consensus with guidance has it along and north of a Benkelman to Cheyenne Wells line. Current forecasted snow ranges from less than inch across the east to 2.5-3 inches across Yuma and Kit Carson county. Where this snow band does develop would create significantly higher snowfall accumulation than is currently forecast due to strong convective signal. Have went ahead and issued a Winter Storm Watch for all three of the Colorado counties as overall confidence is a bit higher that the band may affect those counties as nearly all Hi- Res and deterministic guidance suggests this. There is lower potential that the snow band may set up a bit further east into NW Kansas and SW Nebraska as this is what the ECMWF ensembles have been suggesting for multiple days along with the EFI showing anomalous CAPE values in this area as well. A Winter Weather Advisory has been issued for Sherman, Cheyenne and Dundy counties mainly due to the blowing snow and lesser confidence in this heavy snow band occurring; if confidence does increase in the band occurring in this area then an upgrade may be needed. As for the blowing snow potential, current confidence is highest in blowing snow and strong north winds occurring as this was the primary reasoning for issuing winter weather highlights. Guidance continues to show 40-50 mph winds across the area with the highest being in in the Winter Storm Watch and Advisory counties. Near blizzard to localized blizzard conditions are currently expected. The exact definition of a blizzard is 35 mph wind and quarter mile visibility for 3 hours, I'm overall a bit skeptical if the full three hours can occur mainly due to the intensity of the snowfall. However if the above mentioned band can develop then it may be possible especially if we can get some snow depth in place. The snow will be on the wetter side as well which will make it more difficult to blow once on the ground, therefore limiting visibility issues somewhat. As for the timing, snow will develop across eastern Colorado overnight Saturday into early Sunday morning before spreading into Kansas and Nebraska around sunrise Sunday. The heaviest snow is expected to fall early Sunday morning and last through the late morning hours Sunday before waning in intensity and coverage throughout the day. The strong winds will be ongoing throughout the entire day and even through the night Sunday. Overall, if traveling across western portions of the area hazardous to perhaps even dangerous conditions may occur. Christmas Day, some light snow may still be ongoing from wraparound from the upper level low. Winds will remain gusty from the north at 30-40 mph which may continue blowing snow concerns especially if accumulating snow is in place. High temperatures for the day will be chilly in the low to mid 30s area wide. .LONG TERM...(Tuesday through Saturday) Issued at 301 AM MST Sat Dec 23 2023 At the beginning of the long term period, models forecast the CWA to have a northerly upper air flow being west of an upper air low centered over the KS/MO/NE border area on Tuesday morning. This northerly flow over the CWA is expected to continue through the rest of the day as the models project the upper air low moving eastward along the IA/MO border. On Wednesday, models depict the CWA's flow aloft turning to the northwest by the evening hours as a stronger Canadian upper air low moves down into the western Great Lakes region absorbing the other low into it. For Thursday, the northwestern flow persist over the CWA throughout the day as the aforementioned low departs eastward and an upper air ridge moves towards the CWA. On Friday and Saturday, long term models depict the front part of the ridge being over the CWA and keeping the northwesterly flow aloft. However, the GFS does show a period of a northeasterly upper air flow for the CWA on Friday night due to an upper air low over northern IL reshaping the ridge. The ECMWF does not show this occurring, so will monitor future model runs for better agreement. At the surface, the main concern for impactful weather in the long term period is seen on Tuesday. Models depict a surface low over the eastern KS/NE border as well as a surface high over CO on Tuesday morning generating a pretty good pressure gradient over the CWA. With this gradient, northwesterly winds expect to gust up to around 35 to 40 kts (potentially even higher according to some models) within the CWA during the first half of Tuesday. In addition to these winds, the surface low will bring some chances for wraparound light snow to the CWA (PoPs of ~20-40%) during the Tuesday morning and afternoon hours. Better chances appear to be in the northern half of the CWA at this time before the precipitation chances taper off out to the east as the surface low moves away from the CWA going into the evening. Currently, snowfall accumulations look to be minimal with these chances, but blowing snow may be possible especially in the western portions of the CWA during the first half of the day when the winds are the strongest. Will continue to monitor these conditions going forward. After Tuesday, the remainder of the forecast period looks to stay dry though the GFS hints at a chance for more precipitation possible for the far western portions on Friday evening that the ECMWF does not. Will also monitor this as well in case the signs become more apparent in the long term models. For the temperature forecast, Tuesday's daytime highs expect to range between the middle and upper 30s followed by high temperatures on Wednesday and Thursday being in the upper 30s to middle 40s range. Friday's daytime highs are forecast to be in the middle 30s to lower 40s with Saturday's highs returning to the upper 30s to middle 40s. Low temperatures on Tuesday night look to range between the lower and middle 20s while overnight lows for Wednesday range between the upper teens and lower 20s. Overnight lows on Thursday and Friday nights expect to be in the lower to middle teens followed by Saturday night seeing low temperatures in the middle teens to lower 20s. && .AVIATION...(For the 12Z TAFS through 12Z Sunday morning) Issued at 418 AM MST Sat Dec 23 2023 A potent upper level low is starting to affect the region as mid to upper level clouds stream across the area. Hit or miss light showers are possible through the day today, but confidence in coverage, timing and if there will affect either terminal is very low. Winds will become breezy to gusty from the south as the low moves closer to the area. Overnight Saturday and through the end of the period will see rain/snow chances increase along with lower ceilings and blowing snow. Windy conditions will be present as a cold front moves through the area, a couple hour window for lighter and variable winds along and just behind the front are represented in a tempo for each terminal. && .GLD WATCHES/WARNINGS/ADVISORIES... KS...Winter Weather Advisory from 11 PM MST /midnight CST/ this evening to 5 PM MST /6 PM CST/ Sunday for KSZ001-013. CO...Winter Storm Watch from this evening through Sunday afternoon for COZ090>092. NE...Winter Weather Advisory from 11 PM this evening to 5 PM MST Sunday for NEZ079. && $$ SHORT TERM...Trigg LONG TERM...076 AVIATION...Trigg